A CT method (CT=Computed Tomography) is generally understood to be a transmission tomography unit that uses x-radiation or γ-radiation to transirradiate an examination object from many directions, tomograms of the absorption properties of the examination object being calculated from the measured dose absorption of the radiation. In the case of the PET method (PET=Positron Emission Tomography), a positron-emitting substance is incorporated in the examination object, the positrons forming in conjunction with a shell electron two oppositely directed γ-quanta with 511 keV that can be measured simultaneously.
In the case of the SPECT method (SPECT=Single Photon Emission Computed Tomography), there are incorporated into the examination object single photon emitters whose decay is determined by appropriate detectors. Tomograms of the examination object are calculated in the case of both PET and of SPECT.
A detection arrangement is described in patent specification U.S. Pat. No. 6,448,559 B1. A detection arrangement is shown that is suitable for detecting PET, SPECT and CT signals. The detection arrangement shown there includes a number of absorption layers, the first and thin layer being used to measure low-energy gamma- and x-rays, the second layer being used to measure high-energy gamma radiation, and a third layer being used to measure high-energy 511 keV events. The different absorption layers include various materials, the first layer including a thin CsI(TI) scintillator, and the layers lying therebelow constituting LSO/GSO scintillators. The design of a detection arrangement sketched out there for the combined measurement of CT/PET and SPECT signals is complicated.